Hitherto, there has been proposed a hydraulic control device of this type that controls a hydraulic pressure for a torque converter with a lock-up clutch having a fluid transmission chamber (circulation oil chamber) connected to a torque converter input-side oil passage and a torque converter output-side oil passage, and a lock-up clutch hydraulic pressure chamber (engagement oil chamber) to which a lock-up clutch oil passage is connected (see Patent Document 1, for example). The device includes a lock-up relay valve having a switching portion that switches between a state in which a secondary pressure is supplied to the torque converter input-side oil passage directly and a state in which the secondary pressure is supplied to the torque converter input-side oil passage via an orifice, and a switching portion that switches between a state in which a control pressure obtained by regulating the secondary pressure by a lock-up clutch control valve is supplied to the lock-up clutch oil passage and a state in which supply of the control pressure to the lock-up clutch oil passage is blocked. This allows the hydraulic pressure in the fluid transmission chamber to be switched between high and low levels, and allows the lock-up clutch to be engaged by supplying the control pressure from the lock-up clutch control valve to the lock-up clutch hydraulic pressure chamber with the hydraulic pressure in the fluid transmission chamber at the low level.
With a hydraulic control device of a type in which a pump is actuated using power from a motor, meanwhile, in engaging a lock-up clutch with a motor rotating at a low rotational speed, a sufficient hydraulic pressure for engaging the lock-up clutch may not be obtained from a secondary pressure. Thus, there is proposed a technology for engaging a lock-up clutch using a hydraulic pressure in a line pressure system (see Patent Document 2).